"It's one of the worst days I've ever had in football,"Rooney told MUTV.

"It's hard to take. You have to give Liverpool credit — they played well — but it's difficult to take. Nobody wants to lose, especially in this way, in your own stadium. It's not nice."

The loss at Old Trafford stood out not only for the visitors underlining their credentials as Premier League title challengers, but also United's inability to compete against their north-west rivals.

United's new recruit Juan Mata admitted he was "mad" he was not able to give fans what they deserved in the defeat to Liverpool.

"There are no words to describe your support in the stadium," he wrote in his personal online blog.

"In games like yesterday it makes me mad not being able to give you what you deserve.

"I know there is nothing I can say right now but at least I want you to know how I feel."

Meanwhile, manager David Moyes admitted his first season at Old Trafford after succeeding Sir Alex Ferguson is harder than he ever imagined.

"The job was always going to be hard. Harder? Yes I would say so yes," said the Scot, who has not given up hope of finishing in the top four despite being 12 points adrift of Manchester City, who have two matches in hand.

"It will be very difficult but it's not over yet, so we have to keep working as hard as we can towards trying to do it.

"I've been saying for a while we've given ourselves a long task and a long road to try to get back in it."